1. Field of the Invention
The present invention concerns a punch form, comprising cutting knives and/or scoring rules, whereby the punch form at least partly is dressed with sheet material which is provided in the punch form so that a crack reducing effect on the packaging material is achieved at least in association with the cutting knives and/or scoring rules, and a method for die-cutting packaging material by means of a punch form, comprising cutting knives and/or scoring rules and sheet material which is arranged in the punch form so that a crack reducing effect in the packaging material is achieved at least in association with the cutting knives and/or scoring rules, wherein the packaging material is brought in between said punch form and an anvil, whereby the punch form and the anvil are brought together so that the packaging material will be die-cut. The expression “packaging material” shall here be considered to have a broad meaning and comprise, for example, display material.
2. Description of Related Art
Die-cutting of packaging material may be executed in different ways. Thus, a punch form may be stationary or movable. In the first case the packaging material is fed in between the punch form and an anvil and in the second case the packaging material is fed together with the punch form. In the punching nip, i.e. where the punching takes place, the packaging material is clamped between the cutting knives and/or scoring rules of the punch form and an anvil, and die-cutting occur rapidly.
Cutting means, i.e. cutting knives, scoring rules etc, are generally mounted to a flat or cylindrical bed, a so called flat punch form and rotational punch form, respectively. For each package to be produced a specially designed punch form is required, which is mounted in the present die-cutting apparatus at the time for production.
The punch anvils may have the form of a flat plate or a rotating cylinder.
In the punch nip the cutting knives cut fully through the packaging material while the scoring rules and other means only partly cut through or only deform the packaging material. Generally, score or fold lines are attained, which reduce the bending rigidity in the packaging material.
During die-cutting, cracks easily arise in the die-cut packaging material, especially in the vicinity of the cutting knives and the scoring rules, due to the severe stress in the packaging material.
The die-cut packaging material is pushed out of the punch form by means of resilient elements generally so called rubber ejectors. Such rubber ejectors are generally in direct contact with the packaging material.
After the ejection from the punch form, the die-cut packaging material is passed on and overflow material, so called die-cutting spill, is removed from the packaging blanks, either in connection with the ejection of the packaging blanks from the punch form and leaves the punching nip in question or at a special operation directly afterwards.
When feeding of packaging material to and from the punching nip, during when the punch pressure is activated or deactivated, at ejection and connected removal of spill occur, the packaging material sometimes is deformed in an unwanted way, for example, being bent and/or sheared. As a result a certain percentage of the produced packaging blanks will be damaged, incompletely cleaned from spill or obtain erroneous dimensions. The problems increase with increasing production speed and the level of problem varies for packaging material with different rigidity, moisture levels, etc.
Another problem is damages in the surface of the packaging material caused by the at certain points positioned rubber ejectors, especially at die-cutting of pressure sensitive packaging material and at high production speeds.
These problems may be alleviated by providing a sheet material between the punch form and the packaging material, as described in EP 454753 B1, the content of this is hereby incorporated into this description. The sheet material in question may be dressed on portions of or over the whole punch form, depending on technical requirements and economical considerations.
Also with this solution problems may arise with damaged and incompletely spill cleaned packaging blanks. These problems increase with increasing production speed and increased punching pressure.